The Backhoe is the best piece of equipment to use to dig a big hole. Therefore, Backhoe is what you call someone who gets so caught up in a web of their own lies that he is just digging his own grave. Usually this slander is used most effectively by the party being lied to, when he/she catches the 'Backhoe' lying to his/her face.

Chris: "Dude I just lifted 200lbs right over my head at the gym the other day!"